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The interaction between isothermal aging and long-term reliability of fine pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt%) solder ball interconnects are investigated. In this study, 0.4mm fine pitch packages with 0.3mm diameter Sn-Ag-Cu solder balls are used. Two different die sizes and two different package substrate surface finishes are selected to compare the internal strain impact and alloy effect, especially the Ni effect during thermal cycling. To see the thermal impact on the thermal performance and long-term reliability, the samples are isothermally aged and thermal cycled from 0 to 100oC with a 10minute dwell time. Based on weibull plots for each aging condition, the lifetime of the package reduced approximately 45% with 150oC aging precondition and with longer aging time. Aging at 100oC aging condition show a less impacted but still similar trend. The microstructure evolution is observed during thermal aging and thermal cycling, focused on the microstructure evolution near the package side interface which shows a different phase microstructure transformation between NiAu and OSP surface finishes. Different mechanisms after aging in various conditions are observed and their impact on lifetime reduction is discussed.